Embodiments of the invention relate generally to electron emissive materials and in particular to electrode materials for electric lamps.
Low-pressure metal halide electric discharge plasmas have the potential to replace mercury-based electric discharge plasma used in conventional fluorescent lamps. However, most known electron emission materials in conventional lamps are not chemically stable in the presence of metal halide plasma. Electron-emissive mixtures containing barium oxide have been typically used in mercury discharge lamps. However, the use of barium oxide in metal halide discharge lamps poses certain challenges. The use of barium oxide as a component of lamp electrodes, especially in low-pressure metal halide discharge lamps, is expected to lead to performance issues. This is at least in part due to the reaction of the metal halide with barium oxide, which can lead to the formation of barium halide and a condensed metal oxide. For example, a metal halide discharge medium such as indium bromide may react with an electrode material such as barium oxide to form barium bromide and indium oxide. Such a reaction would lead to a direct reduction in light emitting discharge medium present in the discharge plasma. It would therefore be advantageous to avoid such deleterious reactions in discharge lamps, especially involving the metal halide discharge medium, as it may lead to a reduction in the life of the lamp.